How to initialize static arrays with variable data

[Denis Koroskin]

On Fri, 19 Feb 2010 20:28:20 +0300, Steven Schveighoffer
<schveiguy at yahoo.com> wrote:

> On Fri, 19 Feb 2010 12:15:20 -0500, bearophile  
> <bearophileHUGS at lycos.com> wrote:
>
>> Steven Schveighoffer:
>>
>>> It would be nice to allow this:
>>> int[3] x = [a, b, c];
>>
>> This is allowed now.
>
> Yes, but 1) it allocates the literal on the heap and then throws it  
> away, and 2) it would not be allowed if array literals are only allowed  
> to be immutable.  I'm speaking from the context assuming that array  
> literals are made to be immutable by default.
>
> -Steve

It just *can't* be immutable unless all the variables involved are
implicitly castable to immutable.

And what if I need a *mutable* array? .dup it?

My suggestion would be to be consistent with built-in types. See the
following examples:

auto x1 = 1; // defaults to int, not immutable int
immutable auto x2 = 1; // but immutable also fine
// typeof(x2) = immutable(int)

int a = 42;
immutable auto x3 = a; // you can also construct immutable from a mutable
// variable, if it is implicitly castable to one

Similarly:

auto x1 = [1]; // int[1]
immutable auto x2 = [1]; // immutable(int)[1]

int a = 42;
immutable auto x3 = [a]; // immutable(int)[1]